where \(f\left( {\gamma , m, L} \right) = \ln 2\sqrt{\frac{m}{V(\gamma )}} \left( {{{\log }_2}(1 + \gamma ) - \frac{L}{m}} \right)\) , \(V(\gamma )\)  is the channel dispersion given by \(V(\gamma )=1-(1+\gamma )^{-2}\)  [1]}, and \(Q\left( x \right)\)  is the Gaussian \(Q\) -function.
